Flueric gas-to-liquid interface amplifier

ABSTRACT

A flueric amplifier for controlling the flow of a liquid power jet by means of gaseous control pressure signals. The foregoing is accomplished without any moving parts. Substantially complete segregation of fluids is achieved. The amplifier operates with gaseous pressure-field deflection of a slightly turbulent liquid power jet. The amplifier has infinite input resistance and achieves single stage pressure gains in the neighboord of 25 along with extremely high power gains. The amplifier has a dynamic range and a bandwidth suitable for many applications.

United States Patent 119 Woods 4 May 21, 1974 FLUERIC GAS-TO-LIQUID INTERFACE 3,030,979 4/1962 Reilly .137/835 AMPLIFIER 3,457,935 7/1969 Kantola 137/837 3,545,467 12/1970 Kwok et a1 137/835 X 5] Inventor: Robert Woods, Kensmgton, 3,552,415 1/1971 Small 137/835 A :ThU'tedStat fA [73] sslgnee i z by i xgg fi Primary ExaminerWilliam R. Cline v Army Washington DC Attorney, Agent, or Firm-Edward J. Kelly; Herbert Berl; Saul Elbaum [22] Filed: Oct. 31, 1972 [2l] Appl. No.: 302,453 [57] ABSTRACT A flueric amplifier for controlling the flow of a liquid 52 vs. 01. 137/840 137/806 PWer jet by means P 51 Int. Cl. l l5c 1/14 The fmegoing is ammplished with any 1"- [58] Field of Search 137/803 836 835 837 Pans- Substantially COmPIete. Segregafim fluids 137/838 834 3 261736 is achieved. The amplifier 'operates with gaseous pressure-field deflection of a slightly turbulent liquid 1 [56] References Cited power jet. The amplifier has infinite input resistance and achieves single stage pressure gains in the neigh- UNITED STATES PATENTS boord of 25 along with extremely high power gains. g The amplifier has a dynamic range and a bandwidth 1'] In 3,486,520 12/1969 Hyer Etfll. 137/837 slfltable for many apphcat'ons' 3,563,462 2/1971 Bauer 137/835 1 Claim, 4 Drawing Figures PM vg rs LIQUID SOURCE iATENTEDHAYZI m4 3811.475

' sum 1 ar 2 LIQUID SOURCE PATENTEIImzr m4 SHEET 2 OF 2 APO uqum 6555 no (abs FLUERIC GAS-TO-LIQUID INTERFACE AMPLIFIER RIGHTS OF GOVERNMENT BACKGROUND OF THE INVENTION I 1. Field of the Invention This invention relates to flueric amplifiers and, more particularly, to flueric amplifiersthat provide a gas-toliquid interface.

2. Description of the Prior Art In specialized control applications there frequently exists the need to sense a pneumatic pressure signal that is below ambient pressure and to convert it to a liquid fluidic signal. In such applications it is necessary to provide an interface between the fluidic signals that effectively prevents any flow of liquid into the subambient control port and also prevents entrainment of air bubbles from the control port into the liquid signal over the entire range of operation. This condition of no flow in either direction calls for infinite input resistance characteristics. This has been achieved in fluidic devices with moving parts, but heretofore has not been achieved with flueric devices that utilize no moving parts or fixed separating partitions.

One example of such a specialized control application mentioned above can be found in my co-pending patent application Ser. No. 253,069, now US. Pat. No. 3,771,504, that describes a fluidic fuel injection system for automotive engines. In that system a fluidic circuit that utilizes gasoline as the working fluid is used for sensing, computation, and control functions while a pneumatic pressure signal indicative of engine air consumptionis used as an input to the control circuit. This air consumption signal exists as a subambient pneumatic pressure signal (similar to the venturi vacuum signal in a conventional carburetor) and must be converted to a gasoline fluidic signal for use in the control circuit. The need for the device of the present invention becomes apparent when the need is realized for a gas-liquid interface such that gasoline is not drawn into the vacuum lines and air is not entrained into the liquid. Liquid droplets in the control line cause undue noise in the system and could be drawn into the engine as unmetered fuel. Additionally, entrainment of air bubbles into the fluidic circuitry creates noise in the system and degrades circuit performance.

It is therefore a primary object of the present invention to provide a fluidic gas-to-liquid interface amplifier that effectively'utilizes gaseous pressure signal to control the flow of a liquid while preventing intermixing of the fluids.

An additional object of the present invention is to provide a flueric amplifier that effectively senses a subambient pneumatic pressure signal and converts it to a liquid fluidic signal without the need for moving parts or diaphragms.

A further object of the present invention is to provide a flueric gas-to-liquid interface amplifier that achieves infinite input resistance characteristics without the need for moving parts or diaphragms.

SUMMARY OF THE INVENTION Briefly, in accordance with the invention, a flueric gas-to-liquid interface amplifier having no moving parts is provided which comprisesa supply-port that receives a liquid power jet, a pair of output ports located downstream from the-supply port for exhausting the liquid power jet, a pair of control ports for receiving gaseous control signals, the control ports being in direct communication with the liquid power jet as it issues from the supply'port. Deflection of the power jet is accomplished by the change in the pressure in the control ports while effectively segregating the gaseous signal from the liquid power jet. A pair of top vents are provided to allow entrainment of liquid therefrom by the power jet. Additionally, a pair of bottom vents are strategically located between the top vents and the output port to prevent formation of noise producing reverse flow or circuilating pockets of liquid by the power jet.

The distance between the control ports and the size of the opening of the control ports as well as their angular alignment with respect to the direction of the power jet flow are carefully chosen so as to provide an optimum surface tension bubble between the liquid power jet and the gaseous control signal. The power jet is preferably slightly turbulent so as to provide for total entrainment of any liquid initially present in the control'ports and to maintain the suction effort required for the in- .terface.

BRIEF DESCRIPTION OF THE DRAWING ifier of FIG. 1 under null operating conditions;

FIG. 2b illustrates the amplifier of FIG. 1 subjected to a subambient control'pressure; and

FIG. 3 is a graph of the transfer (input-output) characteristics of the device of the present invention. I

DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic flueric gas-to-liquid interface amplifier of the present invention is shown in FIG. 1. The configuration is similar to a proportional amplifier such as described by D. S. Griffin in the December, 1969 issue of Transactions of ASME, Journal of Basic Engineering at page 734 in an article entitled A Fluid Jet Amplifier with Flat Saturation Characteristics. Shown in FIG. 1 is supply port 10 that accepts a liquid power jet, such as gasoline, from an external source. Immediately downstream of supply port 10 is interface region 40; On either side of interface region 40 is located control ports 12 and 14 that are inclined at an angle a with respect to port 10. Control ports 12 and 14 have externally provided gaseous pressure signals. Immediately downstream of control ports 12 and 14 are a pair of top vents 24 and 26, and immediately below them are a pair of bottom vents 20 and 22. Output ports 16 and 18 are defined by the location of a splitter 42 and are adapted to receive the power jet from supply port 10 that is controlled by apneumatic pressure signal along either or both of control ports 12 and 14.

It is immediately noticed in FIG. 1 that control ports 12 and l4operate over a large area of the power jet as it exits from supply port 10 into interface region 40. The control port opening width 30 is usually defined in terms of the supply port opening 28; for this application, an ideal width 30 was found to be four times the width 28 of the supply port 10. It is apparent that pres-. sure rather than momentum will produce the necessary power jet deflection. Additionally, it is noticed that the downstream separation of the control ports 29 is smaller than is normally found in typical flueric amplifiers. In the device of the present invention-an ideal downstream separation distance 29 was found to be about 2.2 times the width of the supply port opening 28. The control port separation 29 and the small angle a are'selected primarily ,to provide an adequate wall to allow surface tension interface attachment which will be more apparent from the disclosure and discussion hereinafter. The power jet as it progresses from supply port 10 into interface region 40 entrains liquid from top vents 24 and 26 into the bottom vents 20 and 22. Therefore, the top vents 24 and 26 are relatively large to permit entrainment, whereas the bottom vents 20 and 22 are relatively small to ensure that there is no reverse flow or circulating pockets that will produce noise in the system. The partitioned vent design provided by walls 21 and 23 decouples the amplifier operation from the output loading and gives flat saturation characteristics astaught by Griffin and Gebben in A Proportional Fluid Jet Amplifier with Flat Saturation Characteristics and Its Applicaton toGain Blocks, NASA TMX'-l9l5, November 1969.

All vents are connected to a common reservoirtnot shown), whereby the vent pressure can be adjusted by adjusting the reservoir liquid level. It is usually necessary to operate the amplifier with a vent back pressure sufficient to maintain the top and bottom vents fully submerged when the unit is oriented with the power jet on top. The amplifier can be driven with either singlesided inputs (i.e., one control port used as the control pressure input and the other being at ambient pressure) or, under certain conditions, will be able toexcept differential input signals at the control ports.

The operation of the amplifier of FIG. 1 will be more easily understood with reference to FIGS. 2a and 2b. FIG. 2a illustrates the liquid power jet 32'(indicated by P entering interface region40. The liquid flow field is indicated by the shaded area. Gaseous control pressures exist in control channels 12 and 14 and are labeled at ambient or equal pressures. It is seen that as liquid power jet 32 flows through interface region 40 it entrains fluid from top vents 24 and 26 just prior to hitting splitter 42 and being equally divided through output ports-l6 and 18, there being no pressure difference between control ports 12 and 14. Any excess fluid that does not exit through outputs 16 and 18 exhausts through bottom vents 20 and 22. It is seen that there is formed a gas-liquid interface 34 which protrudes partially into the control ports 12 and 14 and creates a surface tension type meniscus that balances the entrainment forces created by turbulent power jet 32. Due to this surface tension, the pressure differential can be supported between the gas and liquid. Since the surface tension at interface 34 can hold various amounts of differential pressure depending upon the surface radius, a

ducts l2 and 14 to power jet 32 thereby causing a jet deflection to either output 16 or 18. It is apparent that inasmuch as there is no input flow into port 12 or 14, the power jet 32 must be deflected by a pressure field and not momentum. FIG. 2aillustrates therefore the situation where no differential control pressure is applied to either of the control ports 12 or 14. At null, the gas pressure in control port 12,-for example, is at ambient pressure while the liquid pressure at region 36 is below ambient and'remains relatively constant over the range of deflection. The radius of the meniscus interface 34 is determined by the pressure differentials.

FIG. 2b illustrates the situation wherein a subambient control pressure P is applied. at control port l2."The power jet 32 thereby deflects towards control port 12 due to the pressure field deflection. The radius of the meniscus interface 34 increases as theliquid pressure I at the region 36 becomesunbalanced-by the application of the control pressure. The amplifier gain is sufficiently high so that the surface tension at meniscus interface 34 can support input pressures at duct 12 varying over a range of 2.5 times the input pressure required to cause saturation of the ouptut. Due to the liquid surface tension, there is no gas flow into the liquid and no liquid flow into the gas; however, a capactive impedance results from the motion of the interface surface when the jet deflects. This compliance is larger than the capacitance of the compressible gas in the control channel of FIG. 1. t

. The device of the present invention has static and dynamic operating characteristics similar to those of many proportional fluid amplifiers and can operate in a range of sizes with almost any liquid. Varsol, water, and MIL-5606 hydraulic oil with nozzle widths from 0.5mm to 2.0mm have been investigated. Weber num-, ber scaling is necessary for proper operation, of the device of the present invention. The Weber number, W is related to the ratio of the inertial forces to the surface Wherein, V isthe liquid power jet velocity, P isthe supply pressure to the power jet, w is the width of the power nozzle, p is the liquid density, and y is the surface tension of the liquid.

The device operates satisfactorily for Weber numbers in the range of about 150 to 250. For Weber numbers below 150, the power jet does not entrain enough flow to keep the liquid from control ports 12 and 14. For Weber numbers above 250, power jet 32 entrains too much flow and air bubbles are entrained from control ports 12 and -14 into the power jet. The optimum Weber number has experimentally been determined to .be about 200. The transfer characteristics normalize for constant Weber number operation.

Other factors must be considered when scaling. For

' example, the size can only be reduced to a point such that the control opening is large enough to prevent liquid droplets from totally attaching to the walls of the control ports causing a capillary effect and erratic be havior. Another restriction-on the size stems from the fact that the fluid velocity cannot be arbitrarily selected :1 eol" lqqw a To 90 phase shift point (0 is about 23 Hz for the 1 mm amplifier; however, the gain is still good at that point. The characteristics shown in FIG. 3 are the static characteristics of an amplifier operating on a commer-' cial solvent with pneumatic control. One amplifier tested had a 1 mm power nozzle operating at a supply pressure of 6.9 kPa at a flow of 28.7 X m lsec.

FIG. 3 is a plot of the transfer characteristics of the device of the present invention operating at a Weber number of 200. FIG. 3 makes it apparent that the device has a blocked load pressure gain of 25. The solid line indicates the region over which there is no inter-.

mixing of fluids; the dashed lines indicate the extended range characteristics in which there'is intermixing of fluids. With the minimum vent pressure, positive (above ambient) control pressures without control flow can be experienced for over one-half of saturation. By.

increasing the vent pressure, this range can be extended to saturation and beyond; however, the subambient range is then decreased.

The interface amplifier of the present invention can also be used with above ambient input pressures. by utilizing an aspirator to convert the above ambient input signals into a subambient control signal. An aspirator can also be used to effect liquid-to-liquid interfaces. Utilizing an aspirator to convert positive liquid pressure to a subambient pneumatic pressure signal, and then using this pneumatic signal as an input to the interface amplifier permits totally different fluids to be interfaced with no intermixing of liquids.

I claim as my invention:

1. A flueric gas-to-liquid interface amplifier having no moving parts, in which deflection of a liquid power jet is efficiently accomplished by a gaseous control signal while segregating said gaseous signal from said liquid power jet, comprising; supply port means for receiving a liquid power jet, an interface region for receiving said liquid power jet from said supply port means, first and second output port means located downstream from said interface region for exhausting said liquid power jet, first and second control port means for receiving gaseous pressure signals, each of said controlport means being aligned at an oblique angle with respect to the direction of flow of said liquid power jet, a pair of top entrainment vent means located between said control port means and said output port means and in open communication with said interface region, a pair of bottom vent means located between said top entrainment vent means and said output port means and inopen communication with said interface region, the cross-sectional area of said top vent means being greater than the cross-sectional area of said bottom vent means, the distance between said control port means on either side of said interface region being approximately 2.2 times the width of the openingof said supply port means into said interface region, the size of the opening of each of said control port means into said interface region being approximately equal to 'four times the width of the opening of said supply port means into said interface region, the Weber number of the liquid of said liquid jet being-in the range of from 150 to 250, and a source of liquid, all said vent means being connected to said source of liquid so as to establish a vent back-pressure sufficient to maintain liquid supply to said vent means. 

1. A flueric gas-to-liquid interface amplifier having no moving parts, in which deflection of a liquid power jet is efficiently accomplished by a gaseous control signal while segregating said gaseous signal from said liquid power jet, comprising; supply port means for receiving a liquid power jet, an interface region for receiving said liquid power jet from said supply port means, first and second output port means located downstream from said interface region for exhausting said liquid power jet, first and second control port means for receiving gaseous pressure signals, each of said control port means being aligned at an oblique angle with respect to the direction of flow of said liquid power jet, a pair of top entrainment vent means located between said control port means and said output port means and in open communication with said interface region, a pair of bottom vent means located between said top entrainment vent means and said output port means and in open communication with said interface region, the cross-sectional area of said top vent means being greater than the cross-sectional area of said bottom vent means, the distance between said control port means on either side of said interface region being approximately 2.2 times the width of the opening of said supply port means into said interface region, the size of the opening of each of said control port means into said interface region being approximately equal to four times the width of the opening of said supply port means into said interface region, the Weber number of the liquid of said liquid jet being in the range of from 150 to 250, and a source of liquid, all said vent means being connected to said source of liquid so as to establish a vent back-pressure sufficient to maintain liquid supply to said vent means. 